CEM

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CEM

^ater ai ^ ness * n t ' le a ' r > but to become as firm as stone underthat f ^ le on ty preparation which puzzolana undergoes, isa °t pounding and sifting, by which it is reduced toeith e arSe . P ow< ^ er • in this state it is beaten up with lime,a ble t ' VUh or w 'tbout sand, which forms a mass of remark-at i ® n acity, that sets under water with great celerity, andfree-st ac< F*' res a strength and hardness equal to those of

th^an° n S? the nations of modern Europe , none have practisedEtutclj ^”*hbng under water to so great an extent as thevaiu,,;, t0 whom we are indebted for the discovery of anotherthis s l 6 mater ‘ a k admirably adapted for aquatic works:tl, an “Stance is called terras, or trass, and is nothing moreIVl- , ! e > or ce bular basalt. It is procured chiefly fromit i s v lejm > Frankfort on the Maine , and Andernacli, whenceIloll * an sported down the Rhine , in large quantities, tot° j.' , f > a Jtd is prepared by grinding and sifting, so asU . Ce to the consistence of coarse sand ; when it isfV° m ln the following manner, with blue argillaceous limeof J® banks of the Scheldt. They take such a quantitys Pr ea d Ume as ma }' be judged sufficient for a week, andand , In a bind of bason, in a stratum about a foot thick,of ( * lnl <'e it with water; this is covered with a stratumor q )r as > °f about the same thickness, and thus left for twofor t xv , ee ,^ a y s > it is then beaten into a mixture, and leftfor < a } -s longer; after which such portions as are wantedOp a / Cor >sumption are taken from the mass, and beatenlerrjrj ln P rev ' ous to being used.—This is the celebratedWork s m ° rtar > with which the mounds and other aquaticil°ll aa( j Use( l» as a defence for protecting the low lands ofThe ’ a ° ains t the incursions of the sea, are consolidated.Osed j n F 10 P°rti° n of the ingredients for terras mortar, asb>e Sarn ‘‘tain in the construction of our water-works, isTiiek.i: as practised by the Dutch, viz., one measure ofWith 0n e anc l two of slacked, in the dry powder, mixed° 0ris isten measure °f terras, and well beaten together to theAnoti, 06 °^. a P aste > using as little water as possible.e 'wap er ® r kind, almost equally good, and considerably°f ’ ls composed of two measures of slacked lime, one

terras ,

j^Uireg ’ and fbree of coarse sand; but this composition> Ces tC° re ^ a bour in beating than the foregoing

..„ ...and pro-

4) c Ujl'ilft _ O & O' T

l 'e huilri ■ e meas ures and a half of excellent mortar. When

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W

p 'th

; n , o ,s composed of rough stones, which leave irre-lnt erstippo 1 _.u. ; • x_

and large cavities, the joints may be filled

Take two mea-measure of terras,

Sl Wes 0 f ^ e mortar, which is thus composed:

° r Pu *‘ acl -d argillaceous lime, half a men°f 8ru ;i j[ T!\ We coarse sand, one of fine sand, and four

'"***<m ~ 1 , ” WUIUV OW1IUJ Viltl V/A «‘ ,v * iv “*

p F hw 63 screene< f and washed, and mix them toge-{ °ma ns ble mortar was a favourite cement among the"’'wka bas been used, ever since their time, in those

Perr ag J” ein a farge quantity of mortar is required.a Tr ; f ®pfar will only acquire its proper hardness underj. ev er arr ^ r 1 Permitted to dry by exposure to the air, it* ,rie had tf 8 tke same degree of hardness as if the same• er y friabi 6611 m ' xe d with good clean common sand, and isr °Ws 0 6 f an< ^ crui ubling; but when kept aways wet,' s ton e * a su bstance something like the concretion inas c °Usid era < j a , Verna ! called stalactite, which substance acquiresto defrit. e , hardness, and in time becomes so exuberant'vij’^gh t; efaCe of tbewaUs.

lif 0 a Ce Hular i , tck terras bas hitherto been prepared

Cal,'' ea u, th kasa b> it appears, from the experiments ofWlu e ^> tvip „ tke c °mmon compact basalt, if previously

Compact

j^alt n v " ul an swer nearly the same purpose. - ,

? a y thp~°? nds in a 'i the districts where coal is raised, ancoal° re be P rocured easily, and calcined with the

In some parts of the Low Countries, coal-ashes are sub-stituted for terras with very good effect, of which the valu-able cendree de Tournay is a striking instance. The deepblue argillo-ferruginous lime-stone of the Scheldt is burntin kilns, with a slaty kind of pit-coal found in the neigh-bourhood. When the calcination of the lime is completed,the pieces are taken out, and a considerable quantity of dustand small fragments remain at the bottom of the kiln. Thisrefuse, consisting of coal-ash, mixed with about one-fourthof lime-dust, is called the cendree, and is thus made intomortar with lime : Put a bushel of the materials into anysuitable vessel, and sprinkle it with as much water as issufficient to slack the lime; then take another bushel, andtreat it in the same manner; and so on, till the vessel isfilled. In this state it remains some weeks, and may be keptfor a much-longer time, if covered with moist earth. Astrong open trough, containing about two cubic feet, is filledabout two-thirds with cement in the above state, and bymeans of a heavy iron pestle, suspended at the end of anelastic pole, is well beaten for about half an hour; at theend of this time it becomes of the consistence of soft mortar,and is then laid in the shade from three to six days, accordingto the dryness of the air. When sufficiently dry, it is beatenagain for half an hour, as before; and the oftener it isbeaten, the better will be the cement; three or four hours,however, are sufficient to reduce it to the consistence of auniform smooth paste. After this period it becomes toostiff, on account of the evaporation of its water, as no moreof this fluid is allowed to enter the composition than whatwas at first employed to slack the lime. The cement, thusprepared, is found in a few minutes to unite so firmly, uponbrick or stone, that still water may be let in immediatelyupon the work, without any inconvenience; and by keepingit dry for twenty-four hours, it has nothing farther to fearfrom the most rapid current.

A composition of a similar nature, is the blue mortar,commonly used in London , for setting the coping of buildings,and other works much exposed to the weather. It is madewith coal cinders and lime, but is seldom prepared with therequisite attention.

Ash-mortar is used in some parts of England, and isprepared by slacking two bushels of fresh meagre lime, andmixing it with three bushels of wood ashes ; this mass is tolie till it is cold, and then to be well beaten ; in this stateit is kept for a considerable time without injury, and evenwith advantage, provided it be thoroughly beaten twice orthrice over before it is used. This cement is superior toterras mortar, in situations alternately exposed to wet anddry; but under water, terras mortar has the advantage.

The scales which are detached by the hammering of red-hot iron, have been long known as an excellent material inwater-works. Mr. Smeaton appears to have been the firstperson who tried the relative strength of mortar made of theoxide of iron, and several other compositions. The scalesbeing pulverized and sifted, and incorporated with lime, arefound to produce a cement equally powerful with puzzolanamortar, when employed in the same quantity. Mr. Smeaton having been successful in his experiments on these materials,was induced to try others of a similar nature. Havingsubstituted roasted iron ore for the scales, he found that thisalso gave to mortar the property of hardening under water,though it required to be used in greater proportions thaneither puzzolana or terras. Two bushels <?f argillaceouslime, two of iron ore, and one of sand, being carefully mixed,produce 3.22 cubic feet cement, fully equal to terras mortar.If the common white lime be employed, it would be advisableto use equal quantities of all the three ingredients